Spatio-temporal dynamics of cavitation bubble clouds in a low frequency reactor: comparison between theoretical and experimental results

The propagation of ultrasound through a liquid induces the growth of incept ions and germs into bubbles. In a low frequency reactor, fragmentary transi ent bubbles emerge due to the acoustic driving. They violently collapse in one cycle and fragment into many smaller bubbles than in turn cavitate, Thi s violent collapse is responsible for the mechanical effects of ultrasounds effects. The latter bubbles gather in a ball-shaped cloud and migrate to p ressure antinodes. During their migration, their nonexplosive collapses mai nly contribute to activate chemical reactions by producing OH. radicals. Ma thematical modelling is performed as a new approach to predict the bubbles field. Through numerical simulation, we determinate emergence sites of mech anically active cavitation bubbles. Calculus are compared with aluminium fo il degradation. The modelling of bubble migration allow us to have an insig ht on the privileged sites of the chemical reactions. Validation of the mod elling is made through direct comparison with chemiluminescence photo. All experiments and computations are made in a 28.2 kHz sonoreactor. (C) 2001 E lsevier Science B.V. All rights reserved.